Color photography



Patented May 25,

a. UNITED STATES "PATENT orrlcsf Alan Gilbert Tull, London; m;- to

Lotta Syndicate Limited, London, mime, a

British company No minin Application December r1, 1940. se-

rial No. 370,557. In Great Britain February 22.

\ sciims.

This invention relates to'the production of coiorphotographs and is concerned primarily with a method of producing a multi-color trans 1 parency or reflection print such as a paper print. The invention also embraces a form oi. multilayer photographic material for the production of such color photographs.

One object of the invention is a simple and effective method of processing a multi-layer or multl-strata material to produce diflerentl'y.

have been made, for instance, on similar-type material. In the case of production of a positive directly on the exposure material, the processed material may be applied to .a paper support to form a reflection print. However, the.

, original exposure being normally made through the support, the finished positive would have to 'be viewed from the'emulsion side to obtain cor-, I

rect lateral rendering and it the material were applied to a paper base the original support. generally Celluloid, would come between the colored image layers and the'paper and would interfere with the correct viewing of the colored images.

The present invention therefore includes the provision of a layer between the original support and the emulsion layers. which is initially transparent and can be or is rendered opaque white or opalescent during the processing, forming a reflective layer enabling the colored images to be viewed by reflection. Such a processed material could be applied to a paper Still further objects relate to a multi-layer photographic material which i designed for the production of a reflection print and embodies a. layer which is. initially transparent and can later be converted to an opaque white layer, and

. to a material embodying a stripping layer whereby the colored image layers'can betransferred to anew support.

The present invention may beapplied to a two-color process and for this purpose a material is preferably utilised having a support of transparent material such as Celluloid on which is coated first a photographicsilver halide emul- "sion'layer which is either non-color sensitised and accordingly'blue sensitive or it may befsensitised for green as well so that the layer is blue green sensitive. Onto this emulsion layer is coated a red or red-yellow sensitive emulsion layer. As this layer remains blue sensitive, a

yellow filter layer is preferably iriterpcsedbe tween the two emulsion, layers to prevent access 'removed from the original support and transof blue light to the red-sensitive layer when exposure is made through the support, or if, as is probable, the red sensitive layer is also strongly green sensitive, an orange or red filter layeris interposedinstead of yellow. I

Such material is exposed in a camera through the support and is processed as described here- "inafter either to' a negative or to a positive which is a natural color reproduction of the original subject, or it may be used as a copy material for reproducingcolored records or color separation records; such 'a colored record might or card supportior convenience and the paper behind the white layer will tend to improve the reflective properties of the whitelayer.

' Such a layer may'consist oi gelatine containing a proportion of colloidal zinc hydroxide giving a layer which is highly transparent. During the processing the material is inserted'in a bath which converts the'zinc hydroxide to an insoluble white ,flnc salt such as nine carbonate or zinc ferrocyanide.

A an alternative to the use of such a layer a stripping layercould be used inthe same position, enabling the colored image layers to be ferred to a new support. Such aiayer may consist of soft gelatine, wax, resin or the like, and is sodesigned that the processing may be carried through to completion on the original support while further soaking, for instance in warm water, enables the colored image layers to be stripped off. 7 V 7 If it is desiredto produce a color transparency such a stripping or reflective layer need not be used or provided. If the material is processed to a positive natural color record, the colored picture may beused directly for projection for instance in'the form of a motion-picture It may however be used for the production of duplicate copies'on a material of the same general type.

It may be preferable however to employ a negative-positive technique it the production of duplicate copies is required. In this procedure 2 the exposure material is processed to a negative without a reversal stage and may be in colors complementary to the layer sensitivity or otherwise, and positive copies in natural colors are printed therefrom, the procedure in this case again not involving a reversal stage.

ored metallic salts or compounds forming th colored images.

The images in the two layers must be processed to different colors and it has been discovered that a conversion bath containing components for the production of a plurality of different colored metallic salts will under suitable conditions deposit the different salts predominantly at different depths of the emulsion layers, thus enabling one color to be deposited primarily in the surface layer and another color predominantly below.

This is particularly noticeable for instance in a reversal technique in which the first developed silver-is not removed and a bath containing a ferric salt and a uranium salt and a carefully controlled quantity of potassium bromide is used. If superposed image layers or strata containing silver ferrocyanide produced from the residual 10% ferric nitrate solution 1 10% uranium nitrate solution 4 10% nitric acid 5 potassium bromide 2 Water to halide are treated in' such a bath, a Prussian blue image is formed exclusively in the surface stratum or layer while there is a red image of uranyl ferrocyanide below that, enabling a natural color picture to be produced on the type of material specifically described above.

In one method of processing such a two layer material, after exposure, for instance in a camera, to produce a natural color picture, the first stage is the development of the latent images in a silver solvent developer such as the following:

The next step is the conversion of the residual halide in both layers into silver ferorcyanide. This may be done by methods well known in the art, which involve the removal of the developed latent image silver by reagents which have no effect on the residual halide, followed by develand this method is preferably employed. The

following conversion bath has been found to'be satisfactory for this purpose:

Formula I! j cc. 5% thiourea solution 10 10% potassium ferrocyanide solution 4 0 Water to 150 The time of treatment is 5 to 15 minutes.

The bath converts the residual silver halide in both layers into silver ferrocyanide without affecting the first developed silver images.

The next step in the processing is the toning of the silver ferrocyanide, that is the conversion of said body into colored metallic compounds or salts, a different compound being produced in the two layers.

In accordance with the present invention this step is performed in a mixed-toning or conversion bath such as. the following:

Formula III The exact proportions of the cdmponents in this bath will depend on the thickness of the I gelatine layers and the characteristics of the gelatine used, and the above formula is accordingly given as an indication of the proportions which might be necessary. The time of immersionin the bath for this method of working is not critical and may be varied from 10 minutes to 30 minutes for optimum results.

The ferric nitrate converts the silver ferrocyanide to Prussian blue and the uranium nitrate converts the silver ferorcyanide to uranyl ferrocyanide which is of red color. It has been found that such a bath can be caused to deposit the Prussian blue for a predetermined depth only below which the uranyl ferrocyanide is deposited, enabling the Prussian blue to be deposited exclusivelyin the surface stratum or layer while the-uranyl ferrocyanide lies immediately below. No full explanation of this phenomenon can be given; it is considered however that in the course of penetration into the layers the ferric salt takes precedence as it gives Prussian blue which is less soluble than the uranyl ferrocyanide. The

uranium nitrate is itself a tanning agent and hardens the gelatine of the emulsion as itpenetrates and this prevents the ferric salt from penetrating into the gelatine, thus limiting the zone of penetration of the ferric salt while below the opment of the latent image to silver and bleaching in an oxidisingbath to form silver ferrocyanide ferrocyanide. This is, broadly speaking the only known method of converting the halide into silverferrocyanide but it has been discovered that the conversion can be more simply effected directly in the presence of a reagent which reverses the relative solubility of the Such a reagent is thiourea, although increase limits the depth of blue and increases uranium salt is effective for the formationof the red image. portion of potassium bromide in the bath exerts a considerable effect on the relative deposits of.

the two toned salts; decrease in the porportion of bromide tending to reduce the proportion ofuranyl ferrocyanide to Prussian blue while an the depth of the. red. Any acceptor for silver ions could be used in place of potassium bromide.

' The appplicant is unable to oifer any explanation as to this phenomenon and directs attention to the fact that the production of a deposit of Prussian blue at any particular point of the upper layer or stratum'is not necessary to prevent the zone of formation of the Prussian blue from extending to any greater depth than'zl's required It is noticeablehowever that the pro-- r for theimage it that is to say the zone of formation of the Prussian blue. can be caused at a suitable stage of the operations.

to occupy a given depth of the emulsion. layers *aasa os is to say the" layer is treated in asolution of a while immediately below lies the zone of forms.-

tion of the uranyl ferrocyanide, irrespective of the quantities of either which are deposited at any one point.

it will beappreciated that the formula given characteristics of the material under treatment and also the thickness of the layers in order-to image in the under layer.

The-final step, apart from whatever washing operaidonsare necessary during and after procthe desired result namely that a blue im-' age is produced in the surface layer and'a red 1 above may have to. be modified according to the. I

red or red-orange sensitising dye in alcohol for, v a a suiliclent period of time for the dyestuirs to penetrate to a limited depth and sensitise that part oi the depth of the emulsion. Such sensi tising dye bath preferably also contains a proportion oi a filter dye which is'such as to penetrate into the layerssuiiiciently to act as a filter dye to prevent the acccss'of blue and green light into the sensitised stratum or depth of emulsion. f

Such fllter dye may he an orangeor red dye according-to the characteristics of the sensitising essingis the removal of the first developed silver and oi any unaflected silversalts' with a suitable reagent such as Farmer's reducer, 'leaving'a reversed color image which correctly reproduces he colors of the o i inal subject within the limdye used. I

As specifically described the image-produced in I the under layer or stratum, consists of uranyl-ferrocyanide. This gives a red image which is not altogether satisiactory'and the present'invention also provides a method of altering the color of s such image by the application of a dye-toning 20 .dye whichawill'mordant either to the uranyl teritations of the two-color process. Asit is desirabie for-the stability or the toned images that the reducer should be acid, and as Farmers re'- I ducercannot be made up with hypo containing the customm'yg potassium matablslllplilte it has been found convenient to adopt the following: A. Hyp j aim; at. Sodium acetate -gms 4 10% acetic acid ccs 4 Water tor. ccs-.. 400

a. 10% potassium ierricyanide.

For useaddl part]! to 3 or 4 parts A.

H the material includes a transparent layer containing zinc hydroxide as referredto above, this is converted to 'an opaque white layerduring the pg, either at aseparate stage, or bythe action of one of the processlng'baths. For example the first developer will normally contain sodium carbonate and this may convert the zinc hydroxide into white zinc carbonate. Alter natively the potassium terrocyanide in the ferrocyanide conversion bath (l lonnula II) may convert the zinc hydroxide into 'white zinc ierrocy-j anlde. Alternatively a separate bath of sodium carbonate or potassium ferrocyanide may be used rocyanide or to a conversion product derived therefrom.

In carrying this part of the invention into eil'ect,'the material, after processing to produce the Prussian blue and uranylferrocyanide images, is treated in a zinc salt conversion bath which converts the uranyl ferrocyanide into zinc ferrocyanide which is an eilective mordant for many dye-toning dyes. Such a bath may contain:

Formula IV Oxalic acid, 5% cc 5 Zinc sulphate, 10% solutions. cc 5 Water to c 20 leavea pure dye image.

'Where the material incorporates a stripping to layer, at the completion of the processing, the

stripping layer in such manner, as by immersion in warm water, asto enable't'he colored image- .materlal istreatedaccording to the nature of the layers to be removed from the original support? I and transferred to a new support, for instance oi .11. however the material is to-be processed to form a colored original from which duplicate col- The .toning dye may be added to this conversion bath or it may be used at a subsequent stage.

dyestuflimage' need not be complete unless dey The invention is also applicable to a three color picture and for this purpose a three layer material isprei'erablyused although a single emulsion could-be used of which the diilerent strata. 'are sensitised for diil'erent spectral regions. It

is conceivable that a mixed toning bath' could be r containing'diil'erent toning compounds for cred copies can be made; the colored ima e lay- 'ers, processed as above described maybe eit on the original transparent support and copied onto a simfllr material by printing'successively' with diii'erently colored printinglights or. with white light or' white'dight. corrected the intcl'positionof corrective filters-so as to have the desired printing values. In this case, it the material includes slayer which can, be rendered opaque White if desired the material is so treated thflt this layer is unaifected.

Although the material hasbeen. described" as consisting of two superimposed 'photographic .emulsionlayers, a} material could also be used consisting of a single orthochromatic emulsionlayer part or the depth of which is sensitised by the controlled penetration of a sensitiser, that the production of three color images and that by suitable selection of such compounds and of the other components in the treatment bath, such as the proportion of potassium bromide, the diiler ent color toning products would be formed or deposited in the diilerent layers or strata.

Preferably however the procedure indicated above for the production oi two differently col' ored images in two layers. is used for two of the colored image'swhlle the third image is produced by other means known in the art.

Various means may be used to obtain this third image and the third image layer could be coated on the opposite side of the material to the other two layers. In this way the-one side of the material could be processed independently .of the other by knownflotation processes in which the material is treated in a bath by floating over the surface thereof in such manner that the under side only is treated.

This procedure enables the third layer to be processed to form a color positive or negative image by dye toning, by color development, either with the color coupling component added to the emulsion at the time of manufacture or with the coupling component added to the developer, by the formation of a dyed gelatin relief image or by other similar processes. As an alternative to a flotation process, the layer or layers on one side may be protected from the action of a treatment bath used for the processing of the layers or layer on the other side, by means of a varnish coating of collodlon, benzyl cellulose or the like. To permit the so-protected layer to be processed the protective layer may be removed by means of a suitable solvent for the varnish; thus acetone could be used for removal of a collodion varnish layer.

In one particularly convenient example all three layers are coated on one side of the support the layer nearest the support containing a proportion of a dye diffusely distributed therein which is capable of being selectively destroyed in the presence of and at the points occupied by a silver image to form a dye image, by the method commonly known as the silver dye-bleach process. This method is particularly applicable to the production of a natural color positive picture on the original exposure material or by copying from a natural color positive, since if the thicurea-ferrocyanide bath (Formula II above) is used for the production of silver ferrocyanide from the residual halide in all, the layers, the same bath will perform the selective destruction of they diffuse dye in the bottom layer if a suitable dye is chosen. Many suchdies are known in the art and need not be listed here.

The material used for carrying this method into effect comprises a transparent support, conveniently of celluloid. On this is coated a noncolor-sensitised silver halide-emulsion which is difiusely dyed yellow with a suitable dye capable of being selectively destroyed in a thiourea bath or other suitable reagent. There is then coated a green sensitive emulsion followed by a red sensitive emulsion. There is no need to provide a yellow filter layer since the yellow-dyed bottom layer will perform the function of preventing access of blue light into the green and red sensitive layers; further if the green sensitive layer is insensitive to red and the red sensitive layer insensitive to green no: filter layer whatever is necessary, giving a material "which is of relatively simple construction. Clear gelatine layers can of course be provided between the emulsionlayrs if desirable to facilitate the subsequent processing. Further there may be interposed between the support and the lowermost emulsion,

a stripping layer, or an initially transparent lay- 7 er which can be rendered opaque white during the processing, as explained above in connection with the two-color process.

Such material is exposed through the base either in a camera to an Original subject or in a printing machine for copying and the first step in the processing is the development of the latent images preferably in asilver solvent developer (FormulaI above). Thereupon the, unaffected silver halide in all three layers is'converted to silver ferrocyanide,- preferably without removal of the first developed silver, by means of a thicurea-ferrocyanide bath such as that given in Formula II above. This bath may itself be of such character as to destroy selectively the yellow dye'in the bottom layer at the points of the original silver image to form a positive yellow image in that layer. If necessary a separate dye-destruction bath could be used at any convenient stage of the processing.

Thereupon the material is treated in a mixed toning bath similar to that given in Formula 111 above but so constituted that the Prussian blue is deposited in the surface layer while the uranyl ferrocyanide is deposited below that while the silver ferrocyanide below that is substantially unaffected, probably on account of the tanning of the overlaying layers.

The material is now treated in a bath which removes the first developed silver images from all the layers as well as the silver ferrocyanide from the bottom layer and any remaining silver above referred'to. Finally the uranyl ferrocyanide may be converted to zinc ferrocyanide and the latter dye toned for instance with Rhodamine G as explained above (Formula IV) or the two baths combined.

This procedure enables a natural color picture to be produced on a multi-layer material of relatively simple construction and by a relatively simple processing technique. The picture obtained could be used as a transparency and the invention is of course applicable to kinematograph records. A print which can be viewed by reflection may be obtained by utilising the layer between the emulsion layers and the support which can be rendered opaque white at a suitable stage in the processing or by means of a stripping layer as above referred to which enables the colored layers to be transferred to a. paper supsilver so as to give anegative color image.

a reagent may be effective only when the image is represented by silver and in that case, the

port.

It is also possible to produce a multi-color negative record,'in which the layers are colored complementarily to the layer sensitivity or otherwise. In this case the latent images are developed in a negative developer, and then the layers are fixed and the developed silver converted by an oxidising bleach bath to silver ferrocyanide. The latter may then be toned in a mixed toning'bath of the character of that given in Formula HI so as to afiect the silver ferrocyanide deposits in the two outer layers. with regard to the lowermost layer, this may be diffusely dyed during manufacture and the colored image therein produced by means of a reagent which is effective at the points unoccupied by Such production of the color image would be efl'ected after development and fixation but before conversion of the silver into ferrocyanide.

, I claim:

1. A method of producing a natural color photograph on a material including a transparent base, ablue sensitive emulsion layer on said base which layer is diffusely dyed yellow, and green andred sensitive emulsion layers coated on said blue sensitive layer, said red sensitive layer being outermost, comprising exposing said material to form-latent images in the different layers, developing such latent images, converting the residual silver halide in said layers into silver ferrocyanide in a. bath containing a ferrocyanide and a I substance which renders the silver ferrocyanide less soluble than the silver halide, toning the silver ferrocyanide in the green and red sensitive layers in a bath containing a ferric salt and uranium salt to form a Prussian blue image in the red sensitive layer and a uranyl ferrocyanide image in the green sensitive layer, and at any stage selectively destroying the yellow dye in the blue sensitive layer at the points occupied by the developed latent image therein.

2. A method of producing a natural color photograph on a material including a transparent base, a layer thereon containing colloidal zinc hydroxide, a blue sensitive, yellow-dyed photographic emulsion layer and green and red sensitive emulsion layers, said red sensitive layer being outermost, comprising exposing such material through the base to form latent images in the three emulsion layers, developing such latent images, converting the residual silver halide in said layers into silver ferrocyanide without atfecting the developed latent images, toning the silver ferrocyanide in the red and green sensitive layers into Prussian blue and uranyl ferrocyanide respectively in a bath containing a ferric salt and a uranium salt, selectively destroying the yellow dye in the blue sensitive layer to form a positive yellow image at any stage and converting the colloidal zinc hydroxide into an opaque white zinc salt.

3. A method of producing colored images in a material embodying an emulsion coat which is differently color-sensitive at different depthsrespectively. comprising exposing such material to produce latent. images in said emulsion coat, developing such latent images, producing silver ferrocyanide images in the diilerent depths of said coat, toning said silver ierrocyanide images in a bath containing a ferric salt and a uranium salt to form in one operation a surface image of Prussian blue and an imageof uranyl ferrocyanide below that and dye-toning said uranyl ferrocyanide.

- 4. A method of producing colored images in a -material embodying an emulsion coat which is diiferently color-sensitive at difierent depths respectively comprising exposing such material to produce latent images in said emulsion coat, developing such latent images, producing silver ferrocyanide images in the different depths of said coat, toning said silver ferrocyanide images in a bath containing a ferric salt and a uraniumsalt'to form a surface image of Prussian blue and an image of uranyl ferrocyanide below that, converting said uranyl ferrocyanide ,to a metallic salt which is a dye-mordant and treating .the material in a dye-toning bath.

ALAN GILBERT TULL. 

